Imo this just an attempt to prime the public for the trial. The defense need a more sympathetic picture of TC than the one that dominates right now. I don't think the press suddenly became overwhelmingly persuasive, I have little doubt they attempted to contact his sister while he was still on the lamb! The timing of her caving to an interview is telling.
I am guessing this was a very scripted interview. Something like this; We need the public to see that Tad also has an older sister, who loves him... Don't mention the minor vic, not once, ever! Do not attempt to excuse his criminal behavior, that will alienate, but do stress that he does not seem to be aware of the gravity of his crimes, and genuinely was trying to help. Stress *remorse*. "
Not even the 12 yr old who reported this whole malarkey, would buy what TC is trying to sell ( via his defense).
His sister did a good job as a part of TC's team. I may have done the same for my brother if asked. (Hard to tell since I never have faced that particular struggle).